Separation of long chain normal paraffin hydrocarbons

ABSTRACT

SEPARATION OF LONG CHAIN NORMAL PARAFFIN HYDROCARBONS FROM HYDROCARBON MIXTURES CONTAINING SAID NORMAL PARAFFIN HYDROCARBONS BY DISTILLATIVE SEPARATION OF A FRACTION HAVING AN END POINT SELECTED TO INCLUDE THE HIGHEST CARBON NUMBER CONSTITUENT OF THE DESIRED NORMAL PARAFFIN HYDROCARBON PRODUCT TO THE EXCLUSION OF THE NEXT HIGHER CARBON NUMBER NORMAL PARAFFIN HYDROCARBON FOLLOWED BY SOLVENT FRACTIONAL CRYSTALLIZATION INVOLVING DILUTION OF SAID FRACTION WITH A SOLVENT AND CHILLING TO A TEMPERATURE EFFECTIVE TO PRECIPITATE THE LOWEST CARBON NUMBER CONSTITUENT OF THE DESIRED NORMAL PARAFFIN HYDROCARBON PRODUCT TO THE EXCLUSION OF LOWER CARBON NUMBER CONSTITUENTS.

"r. A. COOPER ETA SEPARATION OF LONG CHAIN NORMAL PARAFFIN HYDROCARBONS Original Filed May 16, 1967 3 Sheets-Sheet 1 Sept. 1972 COOPER ETAL 27,476

SEPARATION OF LONG CHAIN NORMAL PARAFFIN HYDROGARBONS I Original Filed May 16, 1967 3 Sheets-Sheet 2 T. A. COOPER ET AL Sept. 5, 1972 Y SEPARATION OF LONG CHAIN NORMAL PARAFFIN HYDROCARBONS 3 Sheets-Sheet 3 Original Filed May 16. 19s"! 2 U C v C w. w n m w w w w w m m w. m o

United States Patent Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION (1 Field of the invention This invention relates to a method of separating long chain normal paraflin hydrocarbons of selected chain length from hydrocarbon mixtures including other normal parafiin hydrocarbons, branched chain and cyclic hydrocarbons. This method involves the use of distillative sep aration in combination with cooling in the presence of a solvent to effect fractionation by partial solidification or crystallization. This invention is applicable to the separation of normal paraflins containing from 7 to 35 carbon atoms. It is particularly adapted to the separation of normal paraffin hydrocarbons containing 16 to 25 carbon atoms which are useful in the manufacture of biodegradable detergents, plasticizers and high purity chemical intermediates.

(2) Description of the prior art It has long been known that crude petroleum oils comprise mixtures of paraffin, naphthene, and aromatic hydrocarbons including normal paratiinic hydrocarbons of various' chain lengths. However, the separation of pure normal parafiins having more than about 7 carbon atoms has been difficult'since such mtaerials appear in low concentration in complex mixtures of many hydrocarbon species having close boiling points. 'Schaerer, U.S. 2,603,589, discloses a method of separating straight chain parafiin hydrocarbons having 20 to 60 carbon atoms from wax mixtures by the separation of fractions having a narrow boiling point range of not more than 40 C. (72 F.) followed by cooling to a temperature below that at which the straight chain parafiin hydrocarbons solidify. Recently British specification 1,029,464 has disclosed a method of separating pure normal paraflins having 12 to 16 carbon atoms by distillative separation of a very narrow fraction having a boiling range less than 8 C. (14.4 F.) and preferably less than 6. C. (10.8 F.) followed by crystallization'at Re. 27,476 Reissued Sept. 5, 1972 a temperature between -20 C. and a -30 C. (4 F. and -22 F.) and preferably between -25 C. and 27 C. (13 and 17 F.). It has now been found, in accordance with this invention that pure normal paraffin hydrocarbons may be separated from relatively wide boiling range feed stock with little or no regard for the initial boiling point of the mixture.

SUMMARY OF THE INVENTION This invention relates to a method of separating a product comprising normal paraffin hydrocarbons from a hydrocarbon mixture containing other hydrocarbons including normal paraffins other than those having the chain length of the desired product. For example, a typical gas oil separated by distillation from crude oil is found to have the following tests and normal paraifin content:

ATMOSPHERIC GAS OIL Gravity API 30.5 Distillation, ASTM, F.

IBP 5 12 744 Pour point, F. +50 Analysis, normal parafllns, wt. percent 11-C 0. 1 11"(214 Ill-C15 0.4 n-C 0. 8 n-C 1.7 Ill-C1 1J8 11-01 Ill-C20 3 .7 n'c21 4.1 Ill-C 22 Ill-C23 3.7 Ill-C2 2.8 I1'C25 2.2 H'Czs 1.5 .H-Czq 0.9 11"C28 0.5 nC 0.5 n'c3o 0. 3 11-031 ...F 0-1. n-caz 11 C3 1 Ill-C34 1 n-C 0.1 Ill-C35 Total 32.2

In accordance with this invention, the hydrocarbon mixture is distilled separating a distillate having a boiling range including the highest carbon number constituent of the desired normal parafiin product to the exclusion of the next higher carbon number constituent of said hydrocarbon mixture, that is, the distillation is run to produce distillate of controlled end point. The resulting hydrocarbon distillate is then subjected to solvent fractional crystallization. In the solvent fractional crystallization, the distillate is diluted with up to 5.0 volumes of a solvent at a temperature of complete miscibility of said solvent ud distillate. The diluted distillate is then cooled to a :mperature within the range of 60 to +50 F. and pecifically to the temperature at which the lowest carbon umber constituent of the desired normalparaffins sepaites as a solid from a solution comprising solvent, other ydrocarbons, and normal paraifin hydrocarbons of the ext lower carbon number. In one embodiment of this Wention, a hydrocarbon mixture is distilled to an end oiling point of 650 F., the distillate is diluted with 0.5 2.0 volumes of methylethyl ketone and the diluted mix- 1re cooled to a separation temperature within the range f 20 to +20 F. separating a normal paraffin product ontaining normal parafiins having from to carbon toms of greater than 95 percent purity.

In the fractional crystallization of paratfinic hydrocarons from solvent diluted mixtures, the solvent dilutes the lpernatant liquid and reduces its viscosity so that more )mplete and rapid separation of the supernatant liquid my be effected. Crystallization in the presence of a solent also fosters crystal growth in well formed easily ltered condition. The solvent fractional crystallization E pure normal paraffins may employ the solvents, aparatus and methods employed in the well known solvent ewaxing process which is widely used to lower the cloud nd pour points of lubricating oil fractions. Accordingly, )lvents for use in the process of this invention include etones for example, acetone, methylethyl ketone, methyl propyl ketone, methylisopropyl ketone, methylisobutyl etone and their mixtures. Advantageously the ketone )lvent may be modified by the addition of an aromatic ydrocarbon, for example, benzene or toluene as in solent dewaxing. Cooling is advantageously effected in :raped wall exchangers to maintain high heat transfer ates and prevent plugging. Separation of the normal parflin crystals from supernatant liquid is desirably effected 'ith drum type vacuum filters.

Purity of the separated normal parafiins may be inreased by a repulping operation wherein the separated ormal paraflins are combined with 1.0 to 8.0 volumes of dditional solvent and the normal paraifins then separated tom the repulping solvent at a temperature within the mge of -60 to +50 F. When employing such a reulping operation, the separated repulping solvent is adantageously recycled with the distillate feed to provide t least a part of the solvent used for dilution in the rst separation step. Preferably, in the separation of C C normal paraffins, the separated normal paraflins are :pulped with 2.0 to 6.0 volumes of solvent per volume of ormal paraffins and said normal paraffins are then sepatted from said repulping solvent at a temperature within 1e range of to +20 F.

Since the selection of the separation conditions deterlines the lowest carbon number separated as a solid in te normal paraffin product, normal parafiins of lower llbOIl number remaining in solution with the other hyrocarbons and solvent may be separated in a subsequent :paration step employing a lower temperature. For exmple, normal paraffins of lower carbon numbers may be :parated by cooling the liquid from the first separation to temperature at least 10 F. below the temperature of re first separation. The purity of the separated normal FIGURE 2 is a flow diagram illustrating the separation of two normal paraffin products each product being subjected to a repulping purification.

FIGURE 3 is a representation of the relationship of the end boiling point of a hydrocarbon oil charge with the carbon number of the heaviest normal paraflin in the fraction.

FIGURE 4 is a representation of the relationship of the amount of normal paraffin of a particular carbon number crystallized with the crystallization temperature.

Although the flow diagrams illustrate particular arrangements of apparatus and materials which may be used in the practice of this invention, it is not intended to limit the invention to the particular apparatus of materials described.

Referring to FIGURE 1, a 430 F. IBP gas oil is passed as charge stock through line 1 to distillation tower 2. Distillation tower 2 is operated to separate distillate through line 3 which. distillate has an end point selected to include the highest carbon number normal paraffin in the desired normal paraffin product. For example, the separation of a distillate'having an end point of 650 F. effects inclusion of normal paraffins having carbon numbers up to 20 in the distillate. Higher carbon number normal parafiins and other hydrocarbons boiling above 650 F. are withdrawn as bottoms product through line 4 for use as fuel or cracking stock not shown. The distillate is diluted with solvent, for example, methylethyl ketone from line 6 and recycle filtrate from line 7 and passed to heat exchanger 10. In heat exchanger 10, the oil-solvent mixture is cooled by indirect heat exchange with efliuent filtrate stream in line 11. The cooled mixture from exchanger 10 is passed through line 12 to chiller 13 wherein the temperature is further reduced to cause precipitation of normal paraflin crystals. Exchanger 10 and chiller 13 are advantageously scraped wall double pipe exchangers such as those used in the dewaxing of lubricating oil fractions. The chilled slurry of normal paraflin crystals in solvent diluted oil is passed through line 14 to filter feed tank 15 which serves as a surge tank and also provides time for crystal development. The slurry from tank 15 is Withdrawn through line 16 and passed to vacuum rotary drum filter 17. Separated normal parafiin crystals are washed with solvent introduced through line 20 and discharged through line 21. Filtrate and Washings from filter 17 are withdrawn through line 11 and passed to heat exchanger 10 to provide a portion of the cooling load as described hereinbefore. Eflluent filtrate from exchanger 10 is passed through line 22 to solvent stripper 23 wherein solvent isseparated as distillate in line 24 and stripped filtrate is withdrawn through line 25. The filtrate comprises a deparafiinized 650 F. end point gas oil having a lower pour point than the feed and accordingly-is useful in the manufacture of low pour point arafiins of lower carbon numbers may also be increased y repulping with 1.0 to 8.0 volumes of solvent, and sepalting the repulped normal paraflins from the repulping )lvent at a temperature within the range of 60 to +50 Normal paratfin products comprising normal parafiins E 99 plus weight percent purity may be separated in :cordance with this invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a flow diagram illustrating the separation E normal parafiins with one stage of separation and one :ep of purification by repulping.

fuel oils.

The distillate in line 24 comprising solvent is passed through line 26 to solvent accumulator drum 27 wherein it is collected for reuse. Solvent is withdrawn from drum 27 through lines 28 cooled in chiller 29 and discharged through line 30 to supply the solvent required in lines 6, 20, 33 and 36. Normal parafiin crystals are passed through line 21 and combined with additional solvent from line 33 and passed through line 34 to repulping filter 35.

The normal parafiin crystals are separated and Washed "with additional solvent introduced through line 36.

Washed crystals of normal parafiin are withdrawn through line 3 7 and passed to solvent stripper 38. In solvent stripper 38, solvent is separated as distillate in line 39 and combined with the solvent in line 26 for return to solvent accumulator drum 27. Stripped normal parafiin The intermediate purity normal paraffin stream in line 21 is diluted with solvent from line 33 and charged to rotary filter 35 where additional non-normal paraflin impurities are removed in the filtrate stream. This filtrate removed through line '7 is employed as described heretofore to provide a portion of the dilution solvent.

Referring to FIGURE 2, a wide boiling range gas oil is charged through line 51 to feed fractionator 52. In fractionator 52, low boiling constituents are removed as distillate through line 53. Distillation to remove front end fractions which do not contain desired normal parafiins is employed to reduce the amount of material handled in subsequent processing steps but need not be precise since the subsequent crystallization of normal paratfins is controlled to effect separation between the desired normal parafiin product and normal parafiins of lower carbon numbers. Distillation bottoms from fractionator 52 which may include, for example, normal parafiins having from 12 to 30 carbon atoms, are withdrawn through line 54 and passed to distillation tower 55. Distillation tower 55 is operated to separate a controlled end boiling point distillate such that the distillate includes the highest carbon number normal paraffin desired in the product, for example, C normal parafiin. Higher boiling range hydrocarbons and normal parafiins of higher carbon number than desired in the normal parafiin product are withdrawn as bottoms through line 57. The distillate fraction in line 56 is combined with filtrate from line 60 and solvent from line 61 and passed through chiller 62 wherein the temperature is reduced to crystallize the desired normal paralfin product, for example, normal paraffins in the C to C range. The slurry of crystals in supernatant liquid is passed through line 63 to filter 64 wherein the crystals are separated from filtrate stream withdrawn through line 65. The normal parafiin crystals are washed with additional solvent introduced through line 66 and Withdrawn through line 67. The normal paraflin crystals are then repulped with additional solvent from line 68 and the mixture passed to filter 69 where the repulped purified crystals are separated, washed with additional solvent from line 70, and discharged through line 71. Filtrate comprising washing solvent and a small amount of occluded oil is withdrawn through line 60 and recycled as described above. Normal paralfin product in line 71 is stripped of solvent in solvent stripping tower 72. Product normal parafiins, for example, C to C normal parafiins are withdrawn through line 73 and solvent is recovered as distillate through line 74.

Filtrate in line 65 which comprises normal parafiins haying carbon numbers less than those separated in filter 64 for example C to C normal paraffins and other hydrocarbons and solvent in line 65 is combined with filtrate in line 77 and solvent from line 78 and passed to chiller 79. In chiller 79, the temperature is reduced to a lower level crystallizing the C to C normal parafiins in the mixture and the resulting slurry of crystals in oil is passed through line 80 to filter 81. In filter 81 the separated normal paraffin crystals are washed with additional solvent from line 82 and withdrawn through line 83. Filtrate is withdrawn through line 84 and passed to solvent stripper 8-5 wherein solvent is removed as distillate through line 86 and deparaffinized oil is withdrawn as bottoms through line 87. The separated norm-a1 parafiin crystals in line 83 are repulped with additional solvent introduced through line '90 and passed to filter 91. The repulped crystals are separated in filter 91, washed with additional solvent introduced through line 92, and withdrawn through line 93. The resulting filtrate comprising the removed occluded oil and solvent is recycled through line 77 as described hereinbefore. The washed repulped normal paralfin crystals are passed to solvent stripper 95 wherein solvent is removed as distillate through line 96 and purified C to C normal parafiins are withdrawn through line 97. Solvent from lines 74, 86, and 96 is accumulated in solvent accumulator 98 to supply solvent 6 through line 99 solvent chiller 100 and line 101 to lines 61, 66, 68, 70, 78, 82, and 92.

FIGURE 3 shows the relationship of the end boiling point of a hydrocarbon fraction with the carbon number of the heaviest normal paraflin contained therein. In a fractional crystallization process, the highest carbon number normal paraflin present in the feed crystallizes first and successively lower carbon number constituents separate as the temperature is reduced. Accordingly, in the process of this invention the feed stock is first distilled to separate a distillate having a distillation end boiling point selected to exclude those normal parafiins having higher carbon numbers than desired. By way of example, if it is intended to produce a normal parafiin product containing normal paraffins having 17 and less carbon atoms, FIGURE 3 indicates that the fractional crystallization charge should be distilled to an end point of about 580 to 590 F. When seeking a normal paraflin product containing 20 carbon atoms and less the end point of the distillate is maintained at 650 to 660 F.

As the crystallization temperature is reduced, additional amounts of a given carbon number constituent crystallize out and then lower carbon number constituents begin to crystallize out. This relationship for crystallization of normal paraflins from a hydrocarbon mixture diluted with methylethyl ketone is shown in FIGURE 4. It will be observed that with normal parafiin hydrocarbons containing 20 carbon atoms, crystallization begins at about 42 F. and as the temperature is reduced additional C normal paraffins crystallize until at a temperature of about 8 F. all C normal parafiins have crystallized. Crystallization of 19 carbon atoms normal parafiins begins at about 32 and all C normal paraflins are crystallized by the time the temperature reaches 2 F. Accordingly recovery of the highest molecular weight normal paraifin in the product is regulated by the end boiling point of the charge to the fractional crystallization and the lowest molecular weight normal paraflin in the product is controlled by fractional crystallization temperature. FIGURE 4 may be used to estimate the recovery of each normal paraflin component of a charge stock for a given fractional crystallization temperature and from an analysis of the charge, the expected yield of normal paraffim product can be determined. For example, separation at 0 F. is indicated to recover all of the C and higher normal paraffins in the charge, 93% of the C normal paraffins, 59% of the C normal parafiins, 26% of the C normal parafiins and essentially none of the C and lower normal paraflins. Separation temperatures below 40 C. are indicated to be required to recover about half of the C normal paraffins which temperature is about the economic limit for solvent fractional crystallization at this time. The upper limit of normal paraffin recovery is about the C normal parafiins since the transition to microcrystalline waxes occurs at about this level.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example I In an example of the process of this invention, a gas oil fraction having an end boiling point of 637 F. is separated by distillation and charged to a solvent fractional crystallization system employing methylethyl ketone (MEK) as solvent at the conditions and with the results shown in Table I following:

I 7 n-C1g 2.8 n-C I 3.6 n-C 1.6

Total 11.9 )perating conditions Primary fractional crystallization Solvent MEK Dilution, vol. solventzvol. charge 1:1 Wash, vol. solventzvol. charge 1:1 Filtering temperature, F Repulping Solvent MEK Dilution, vol. solventzvol. charge 4:1 Wash, vol. solventzvol. charge 3:1 Filtering temperature, F. 10 Iormal paraflin product Yield vol. percent charge 9.5 Analysis, n-paraffins, wt. percent Ill-C 0 n-Cm 0.9 n-C n-C n-C n-C 19.4

Total 97.7

Analysis of the results in Table I shows that although he gas oil charge stock contains over 88% non-normal iarafiin hydrocarbons, the separated product contains 7.7 wt. percent normal paraffins and 96.8 percent C -C iormal parafiins. It will further be noted that although he feed stock contains substantial amounts of C and 3 normal paraflins, the separated product is free of C lormal parafiins and contains only about 6 percent of he C normal parafiins contained in the feed.

Example H In this example a gas oil is distilled to a 623 F. end ioint to include C normal paraflins but to exclude higher ioiling normal paraffins. The resulting distillate is then ubjected to solvent fractional crystallization at the conlitions and with results shown in the following Table II.

TABLE II Gas oil Jharge tests:

Bolling range, F.:

Initial boiling point End point Analysjis, n-parafiins, Wt. percen Test A Test B bperating conditions Primary fractional crystallization:

Solvent rob- P1 Repulping:

olvent Dilution, vol. solventzvol. charge..." Wash, vol. solventwol. charge Filtering temperature, F Iormal parathn product:

Yield vol. percent charge Analysis, n-paraffin wt. percent:

Table II shows that fractional crystallization at 0 F. :roduces a product comprising 99.0 wt. percent normal araflins or 96.1 percent C -C normal paraflins. Frac- Cit 8 tional crystallization at +10 F. at the same dilution and wash solvent ratios gives a normal parafiin product of 97.5 wt. percent normal paraffins comprising 90.3 wt. percent C and C normal paraffins.

Example III The ability of the present invention to employ a feed stock with a considerable amount of light material therein is shown in the treatment of a light gas oil distilled to have a boiling range of 447 to 616 F. This feed stock is subjected to fractional crystallization in the presence of methylethyl ketone solvent at the conditions with the results shown in the following Table III:

TABLE III Charge tests Gas oil Boiling range, F.

Initial boiling point 447 End point 616 Analysis, n-paraflins, wt. percent Il-Cn 0.1 Ill-C12 0.2 Ill-C13 09 Ill-C 4 1.5 II-C15 1.6 n-C 1.8 Il-C17 1.6 III-C13 2.1 Il-C1 2.5 II-Cgo 0.7

Total 13.0 Operating conditions Primary fractional crystallization Solvent MEK Dilution, vol. solventzvol. charge 0.5 :1 Wash, vol. solvent:vol. charge 1:1 .Filtering temperature, F. -10 Repulping Solvent MEK Dilution, vol. solventzvol. charge 4:1 Wash, vol. solvent:vol. charge 3:1 Filtering temperature, F. -10 Normal paraflin product Yield vol. percent charge 10.7 Analysis, n-paraffins wt. percent l'l-Cn 0 Il-C 0 n'C13 o n-C 0 11'015 0-4 1:1-C13 2-3 n-C n-C 26.4 H-C19 n-czo Total 97.7

Reference to Table III shows that although the feed stock contains substantial amounts of 0 -0 normal parafiins, none of these normal paraflins appear in the normal paraflin product, and the normal parafiin product comprises 95.0% C to C normal parafiins.

We claim: 1. A method of separating normal parafiin having from 15 to 20 carbon atoms from a gas oil containing such paraflins and other hydrocarbons which comprises:

(1) distilling said gas oil, and separating a distillate comprising normal paraffins having from 15 to 20 carbon atoms and having a boiling range from substantially the initial boiling point of said gas oil and including the highest carbon number constituent of the desired normal parafiin' product to the substantial exclusion of the next higher carbon number normal paraflin' constituent of said gas oil,

(2) diluting said distillate with up to 5.0 volumes of a solvent at a temperature of complete miscibility of said solvent and said distillate forming a diluted distillate,

(3) cooling said diluted distillate to a temperature within the range of 60 to +50 F. and at which the lowest carbon number constituent normal paraffin of the desired normal paraffin product separates as a solid comprising said product from a solution comprising solvent, other hydrocarbons, and normal paraflins of lower carbon numbers.

(4) and separating said solid comprising said normal parafiin product from said solution in a [yield] purity of at least 95 weight percent.

2. The process of claim 1 wherein said distillate has an end boiling point of 650 F., said distillate is diluted with 0.5 to 2.0 volumes of said solvent, and said diluted distillate is cooled to a separation temperature within the range of -20 to +20 F.

3. The process of claim 1 wherein said solvent comprises a ketone selected from the group consisting of acetone, methylethyl ketone, methyl n-propyl ketone, methyl-isopropyl ketone, methyl-isobutyl ketone and their mixtures.

4. The process of claim 3 wherein said solvent comprises said ketone and an aromatic hydrocarbon selected from the group consisting of benzene and toluene.

5. The process of claim 1 wherein the separated normal paratfins are repulped with 1.0 to 8.0 volumes of solvent, said normal parafiins are separated from the repulping solvent at a temperature within the range of -60 to +50 F., and separated repulping solvent is recycled to provide at least a portion of said solvent used for dilution of said distillate.

6. The process of claim 5 wherein said separated normal parafiins are repulped with 2.0 to 6.0 volumes of solvent and said normal parafiins are separated from said 10 repulping solvent at a temperature within the range of 25 to +20 F.

7. The process of claim 1 wherein said solution comprising solvent, other hydrocarbons and normal parafiins of the next lower carbon number is cooled to a temperature at least 10 F. below the temperature to which said diluted distillates is cooled effecting separation of said normal paraffins of lower carbon number as a solid from remaining solution comprising solvent and other hydrocarbons.

8. The process of claim 7 wherein the separated normal paraffins of lower carbon numbers are repulped with 1.0 to 8.0 volumes of solvent, said normal paraflins of lower carbon numbers are separated from the repulped solvent at a temperature within the range of 60 to F. and separated repulping solvent is recycled in admixture with said solution.

References Cited The following references, cited by the Examiner, are of record in the patented file of this patent or the original patent.

UNITED STATES PATENTS 3,409,514 11/ 1968 Drapeau et a1 260-676 1,951,780 3/ 1934 Voorhees 62-58 2,603,589 7/1952 Schaerer 208-24 2,815,364 12/1957 Green 260-676 3,067,270 12/1962 Weedman 203-48 FOREIGN PATENTS 525,388 8/ 1940 Great Britain 260-676 HERBERT LEVINE, Primary Examiner US. Cl. X.R. 

